Summary of some common error and exception handling methods in Java

Some common mistakes and solutions. I am a novice, and I have recorded every error I encounter.

1. 404 error

description The requested resource (/Struts2_0100_Introduction/hello.action) is not available.

Check the Manager Deployments first so that it can be opened (NullPointerException occurs cannot be opened), the main reason is that the server backs up before each permission, and cannot correct the error in time after modifying it. (If Backup is checked, change it to delete)

2. Error configuring application listener of class org.springframework.web.context.ContextLoaderListener

java.lang.ClassNotFoundException: org.springframework.web.context.ContextLoaderListener

The port is written wrong, the port is 3306, I wrote

instead of 8080

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